As illustrated in FIG. 1 a typical dual-band PIFA has a radiating element RE connected to the phone printed circuit board (PCB) PP, which comprises a ground plane, through feed FT and shorting ST tabs (or pins). The radiating element RE also comprises a slot SO having approximately a U shape. Such an antenna is notably described in the patent document US 2001/0035843.
The SAR of such a dual-band PIFA can be simulated using a truncated flat phantom material layer PML and a skin layer SL such as the ones shown in FIG. 2. A flat phantom material layer PML is effectively considered to be more appropriate for comparative simulations than a curved alternative since a constant spacing is maintained between the phantom material layer and the PCB.
Examples of the relative dielectric constant and conductivity of the phantom PML and skin SL layers are given in the following Table 1 both for GSM and DCS standards.
TABLE 1PhantomSkinRelativeRelativeFrequencydielectricConductivitydielectricConductivityBandconstant εprσp (S/m)constant εsrσsGSM41.50.94.20.0042DCS401.44.20.00084
To minimise reflections at the truncation surfaces of the phantom material layer, these surfaces are defined as impedance boundaries, having the characteristic impedances of the dielectrics used. The characteristic impedance of a lossy dielectric is given by the following relation:
      Z    0    =            μ              ɛ        -                  jσ          /          ω                    where                μ is the magnetic permeability of the media,        ε the electric permittivity of the media,        σ is the bulk conductivity, and        ω is the angular frequency (i.e.=2π times the frequency).        
Using this relation, the characteristic impedances of the phantom PML and skin SL layers are given in the following Table 2 both for GSM and DCS standards.
TABLE 2Phantom impedanceSkin impedanceFrequency (MHz)(Ω/square)(Ω/square)90054.35 + j12.06183.83180057.06 + j9.68 
An example of simulated SAR in the GSM (a) and DCS (b) bands is shown in FIG. 3. The SAR is sketched in W/kg and corresponds to an accepted power normalised to 1 W.
A known problem is that small dual-band PIFA antennas are required for diversity operation. Such antennas are narrowband, only operate over a limited number of bands, and exhibit high SAR compare with larger antennas (SAR is a local quantity).